1. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Section 1 The Development of a New Atomic Model Properties of Light The Wave Description of Light Electromagnetic radiation is a form of energy that exhibits wavelike behavior as it travels through space. Together, all the forms of electromagnetic radiation form the electromagnetic spectrum.

2. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Electromagnetic Spectrum Section 1 The Development of a New Atomic Model

3. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Section 1 The Development of a New Atomic Model Properties of Light, continued Wavelength (λ) is the distance between corresponding points on adjacent waves. Frequency (ν) is defined as the number of waves that pass a given point in a specific time, usually one second.

4. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Section 1 The Development of a New Atomic Model Properties of Light, continued Frequency and wavelength are mathematically related to each other: c = λν In the equation, c is the speed of light (in m/s), λ is the wavelength of the electromagnetic wave (in m), and ν is the frequency of the electromagnetic wave (in s −1 ).

5. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Wavelength and Frequency Section 1 The Development of a New Atomic Model

6. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Section 1 The Development of a New Atomic Model The Photoelectric Effect The photoelectric effect refers to the emission of electrons from a metal when light shines on the metal. The Particle Description of Light A quantum of energy is the minimum quantity of energy that can be lost or gained by an atom.

7. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Photoelectric Effect Section 1 The Development of a New Atomic Model

8. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Section 1 The Development of a New Atomic Model The Photoelectric Effect, continued The Particle Description of Light, continued German physicist Max Planck proposed the following relationship between a quantum of energy and the frequency of radiation: E = hν E is the energy, in joules, of a quantum of radiation, ν is the frequency, in s −1, of the radiation emitted, and h is a fundamental physical constant now known as Planck’s constant; h = 6.626 × 10−34 J s.

9. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Section 1 The Development of a New Atomic Model The Photoelectric Effect, continued The Particle Description of Light, continued A photon is a particle of electromagnetic radiation having zero mass and carrying a quantum of energy. The energy of a particular photon depends on the frequency of the radiation. E photon = hν

10. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Section 1 The Development of a New Atomic Model The Hydrogen-Atom Line-Emission Spectrum The lowest energy state of an atom is its ground state. A state in which an atom has a higher potential energy than it has in its ground state is an excited state.

11. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Section 1 The Development of a New Atomic Model The Hydrogen-Atom Line-Emission Spectrum, continued When investigators passed electric current through a vacuum tube containing hydrogen gas at low pressure, they observed the emission of a characteristic pinkish glow. When a narrow beam of the emitted light was shined through a prism, it was separated into four specific colors of the visible spectrum. The four bands of light were part of what is known as hydrogen’s line-emission spectrum.

12. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Hydrogen’s Line-Emission Spectrum Section 1 The Development of a New Atomic Model

13. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Section 1 The Development of a New Atomic Model Bohr Model of the Hydrogen Atom Niels Bohr proposed a hydrogen-atom model that linked the atom’s electron to photon emission. According to the model, the electron can circle the nucleus only in allowed paths, or orbits. The energy of the electron is higher when the electron is in orbits that are successively farther from the nucleus.

14. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Section 1 The Development of a New Atomic Model When an electron falls to a lower energy level, a photon is emitted, and the process is called emission. Energy must be added to an atom in order to move an electron from a lower energy level to a higher energy level. This process is called absorption. Bohr Model of the Hydrogen Atom, continued

15. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Preview Lesson Starter Objectives Electrons as Waves The Heisenberg Uncertainty Principle The Schrödinger Wave Equation Atomic Orbitals and Quantum Numbers Section 2 The Quantum Model of the Atom

16. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Photon Emission and Absorption Section 1 The Development of a New Atomic Model

17. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Section 2 The Quantum Model of the Atom Electrons as Waves French scientist Louis de Broglie suggested that electrons be considered waves confined to the space around an atomic nucleus. It followed that the electron waves could exist only at specific frequencies. According to the relationship E = hν, these frequencies corresponded to specific energies—the quantized energies of Bohr’s orbits.

18. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Section 2 The Quantum Model of the Atom Electrons as Waves, continued Electrons, like light waves, can be bent, or diffracted. Diffraction refers to the bending of a wave as it passes by the edge of an object or through a small opening. Electron beams, like waves, can interfere with each other. Interference occurs when waves overlap.

19. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Section 2 The Quantum Model of the Atom The Heisenberg Uncertainty Principle German physicist Werner Heisenberg proposed that any attempt to locate a specific electron with a photon knocks the electron off its course. The Heisenberg uncertainty principle states that it is impossible to determine simultaneously both the position and velocity of an electron or any other particle.

20. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Section 2 The Quantum Model of the Atom The Schrödinger Wave Equation In 1926, Austrian physicist Erwin Schrödinger developed an equation that treated electrons in atoms as waves. Together with the Heisenberg uncertainty principle, the Schrödinger wave equation laid the foundation for modern quantum theory. Quantum theory describes mathematically the wave properties of electrons and other very small particles.

21. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Section 2 The Quantum Model of the Atom The Schrödinger Wave Equation, continued Electrons do not travel around the nucleus in neat orbits, as Bohr had postulated. Instead, they exist in certain regions called orbitals. An orbital is a three-dimensional region around the nucleus that indicates the probable location of an electron.

22. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Section 2 The Quantum Model of the Atom Atomic Orbitals and Quantum Numbers Quantum numbers specify the properties of atomic orbitals and the properties of electrons in orbitals. The principal quantum number, symbolized by n, indicates the main energy level occupied by the electron. The angular momentum quantum number, symbolized by l, indicates the shape of the orbital.

23. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Section 2 The Quantum Model of the Atom Atomic Orbitals and Quantum Numbers, continued The magnetic quantum number, symbolized by m, indicates the orientation of an orbital around the nucleus. The spin quantum number has only two possible values—(+1/2, −1/2)—which indicate the two fundamental spin states of an electron in an orbital.

24. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Shapes of s, p, and d Orbitals Section 2 The Quantum Model of the Atom

25. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Section 3 Electron Configurations Objectives List the total number of electrons needed to fully occupy each main energy level. State the Aufbau principle, the Pauli exclusion principle, and Hund’s rule. Describe the electron configurations for the atoms of any element using orbital notation, electron- configuration notation, and, when appropriate, noble- gas notation.

26. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Section 3 Electron Configurations Electron Configurations The arrangement of electrons in an atom is known as the atom’s electron configuration. The lowest-energy arrangement of the electrons for each element is called the element’s ground- state electron configuration.

27. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Relative Energies of Orbitals Section 3 Electron Configurations

28. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Section 3 Electron Configurations Rules Governing Electron Configurations According to the Aufbau principle, an electron occupies the lowest-energy orbital that can receive it. According to the Pauli exclusion principle, no two electrons in the same atom can have the same set of four quantum numbers.

29. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Section 3 Electron Configurations Rules Governing Electron Configurations, continued According to Hund’s rule, orbitals of equal energy are each occupied by one electron before any orbital is occupied by a second electron, and all electrons in singly occupied orbitals must have the same spin state.

30. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Section 3 Electron Configurations Representing Electron Configurations Orbital Notation An unoccupied orbital is represented by a line, with the orbital’s name written underneath the line. An orbital containing one electron is represented as:

31. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Section 3 Electron Configurations Representing Electron Configurations, continued Orbital Notation An orbital containing two electrons is represented as: 1s1s He The lines are labeled with the principal quantum number and sublevel letter. For example, the orbital notation for helium is written as follows:

32. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Section 3 Electron Configurations Representing Electron Configurations, continued Electron-Configuration Notation Electron-configuration notation eliminates the lines and arrows of orbital notation. Instead, the number of electrons in a sublevel is shown by adding a superscript to the sublevel designation. The helium configuration is represented by 1s 2. The superscript indicates that there are two electrons in helium’s 1s orbital.

33. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Section 3 Electron Configurations Representing Electron Configurations, continued Sample Problem A Solution The number of electrons in a boron atom is equal to the sum of the superscripts in its electron- configuration notation: 2 + 2 + 1 = 5 electrons. The number of protons equals the number of electrons in a neutral atom. So we know that boron has 5 protons and thus has an atomic number of 5. To write the orbital notation, first draw the lines representing orbitals. 1s1s 2s2s 2p2p

34. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Section 3 Electron Configurations Representing Electron Configurations, continued Sample Problem A Solution, continued Next, add arrows showing the electron locations. The first two electrons occupy n = 1 energy level and fill the 1s orbital. 1s1s2s2s 2p2p

35. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Section 3 Electron Configurations Representing Electron Configurations, continued Sample Problem A Solution, continued The next three electrons occupy the n = 2 main energy level. Two of these occupy the lower- energy 2s orbital. The third occupies a higher- energy p orbital. 1s1s2s2s 2p2p

36. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Section 3 Electron Configurations Elements of the Second Period In the first-period elements, hydrogen and helium, electrons occupy the orbital of the first main energy level. According to the Aufbau principle, after the 1s orbital is filled, the next electron occupies the s sublevel in the second main energy level.

37. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Section 3 Electron Configurations Elements of the Second Period, continued The highest-occupied energy level is the electron- containing main energy level with the highest principal quantum number. Inner-shell electrons are electrons that are not in the highest-occupied energy level.

38. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Writing Electron Configurations Section 3 Electron Configurations

39. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Section 3 Electron Configurations Elements of the Third Period After the outer octet is filled in neon, the next electron enters the s sublevel in the n = 3 main energy level. Noble-Gas Notation The Group 18 elements (helium, neon, argon, krypton, xenon, and radon) are called the noble gases. A noble-gas configuration refers to an outer main energy level occupied, in most cases, by eight electrons.

40. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Orbital Notation for Three Noble Gases Section 3 Electron Configurations

41. Chapter 4 © Houghton Mifflin Harcourt Publishing Company Orbital Notation for Argon and Potassium Section 3 Electron Configurations

42. © Houghton Mifflin Harcourt Publishing Company End of Chapter 4 Show